Have had several of the old aluminum wired Apple Keyboards (I assume that's what is being discussed?) and always liked them. However, they could be pretty weird, even when new. One of them only worked on the left USB port of my 2013 MacBook Air. Then one day, without any apparent reason, it would no longer work on the left port but *would* work on the right port. Worked fine on any port of my 2012 Mini though.
Did some Googling at the time and found similar stories without much explanation. Later, I read that they were sensitive to voltage, and small variations could prevent them from working. Could that explain what you saw in the lab?